1. Technical Field
The present invention generally relates to damping systems and, more particularly, to an apparatus for reducing vibrations in a latch mechanism of a telescoping structure such as those found in large diameter spacecraft antennas.
2. Discussion
In many situations where trusses, girders, or beams are needed, a conventional solid beam is unsuitable. It is essential that the structural member used be more light-weight, especially in those cases where transportation presents difficulties. It may be further desired that the element be collapsible to a compact size, and, finally, readily erectable upon deployment. These considerations are particularly crucial for operations in outerspace, such as deployment of antenna or space platforms. Launch is feasible only for those structures which are light-weight and compact. The addition of each unit of mass or volume is extremely expensive.
The size of orbital space structures is, at present, limited to the cargo volume of the National Aeronautics and Space Administration's space shuttle vehicle and/or launch vehicle payload volume. These vehicles have demonstrated the feasibility and practicality of transporting various payloads for deployment into spacial orbits about earth. It is now contemplated that larger packages may be transported and multiple segments assembled, expanded and/or added onto previously or subsequently launched payloads. It has previously been demonstrated that folded compact, rolled, and inflatable payloads may be compactly packaged for launch and deployed when placed in earth orbit. This procedure has proved especially effective for weather and communication satellites, antennas, and the like. Large volume truss structures and the like which can be collapsed for storage and transported in a relatively small volume and subsequently deployed at the sight of use to envelope a large volume and/or form planar, curved, and contoured surfaces appear to have valuable future use in space, on earth, and/or on other planets.
A truss structure is generally composed of straight members subject preferably to longitudinal compression, tension, or both. The members are disposed so as to make the structure rigid under anticipated loads. Truss structures are particularly desirable in space application because of their high strength and/or stiffness and low mass. Packaging a truss structure by the use of telescoping members introduces axial compliance, thereby decreasing the stiffness of the truss. In order to optimize stiffness and strength, a latch mechanism is employed. The latch mechanism should be sufficiently strong to hold the truss structure in its expanded configuration though it should be simply released to allow the truss structure to be recollapsed.
Some previously employed expandable truss structures have failed to use regulation mechanisms such as dampers, between expanding component parts. These aerial truss structures are thus deployed unconstrained. Uncontrolled, expandable trusses which are devoid of regulating features may exhibit kinematic anomalies during deployment or become distorted and prevent attainment of the desired final functional state or configuration. Further, induced oscillations of the device may prevent operation in a desired mode prior to settling.
Dampers of varying configurations have been used to various degrees in the automotive industry. For instance, U.S. Pat. No. 4,869,476 entitled "Electrically Controlled Viscous Elastic Spring" to Shtarkman and assigned to the Assignee of the present invention and incorporated by reference herein describes a spring for resisting relative movement of parts and for urging the parts to an initial, equilibrium position when the parts are moved therefrom. The spring uses a fluid, such as an electro-rheological fluid or a magnetic fluid, to provide a variable spring rate and a variable load-carrying capacity. The resistance to flow of these fluids varies as a function of the magnitude of either an electric field or a magnetic field applied to the fluid.
Another known device using electro-rheological fluid for damping is disclosed in U.S. Pat. No. 4,896,752 entitled "Vehicle Strut" to Shtarkman and assigned to the Assignee of the present invention which is also incorporated by reference herein. This reference discloses a strut for use in a suspension system wherein the spring and damping characteristics of the strut are controlled, in part, by an electro-rheological fluid disposed within fluid chambers in the strut. When the viscosity of the fluid is varied by changing the magnitude of the electric field applied to the fluid, the spring rate of the strut is varied.
Further, U.S. Pat. Nos. 4,942,947, 4,992,190, 5,167,850, 5,176,368 all to Shtarkman, and U.S. Pat. Nos. 5,257,681, 5,354,488, 5,367,459, 5,517,096 and 5,655,757 to Shtarkman, et al., each of which is assigned to the Assignee of the present invention and is incorporated by reference herein, disclose devices utilizing fluid compositions which are responsive to an electric or magnetic field. By controlling the magnitude of the field, the spring and damping characteristics of the devices can be manipulated.
In view of the foregoing, it would be desirable to provide an apparatus for damping vibrations in the latch mechanism of a telescoping component by utilizing a fluid responsive to an electric or magnetic field.